Mass gain is fairly simple with a solid program. The key is what you want to do with your exercises specifically working towards your goals. Hash out a few goals first and then we can go over a routine (coupled with a good diet) that will help you gain mass.

As it is, that routine is fairly week namely.. it doesn't have any heavy full body lifts as explosive movements exclude heavy squats and DLs which are going to be your main "mass builders" as they stimulate huge hormone release. Explosive exercise is good overall though. Circuits are not particularly good at building mass. You're better off with pure strength work with a 3-4 upper body exercises combined with 2 lower body/full body lifts. So yeah. That's just if you wanted a simple critique.